This project is on the interaction of tumor cells and host defense cells. Current studies include the depression of macrophage chemotaxis that occurs in tumor-bearing patients and experimental animals; the increase in chemotactic and tumoricidal activity that occurs in BCG-infected tumor-bearing mice; the characterization of a chemotactic factor produced by growing tumors in vitro, which could lead to accumulation of macrophages in tumor sites; and the isolation of lymphotoxin, a protein produced by mitogen or antigen-stimulated lymphocytes that is toxic for tumor cells. BIBLIOGRAPHIC REFERENCES: Meltzer, M.S. and Oppenheim, J.J.: Bidirectional amplification of macrophage-lymphocyte interactions: Enhanced lymphocyte activation factor production by activated adherent mouse peritoneal cells. J. Immunol. 118: 77-82, 1977. Ruco, L.P. and Meltzer, M.S.: Macrophage activation for tumor cytotoxicity: Induction of tumoricidal macrophages by supernatants of PPD-stimulated BCG-immune spleen cell cultures. J. Immunol. in press. 1977.